Producing gears with the proper lead angle, profile, concentricity, size and surface finish is a major problem for the gear manufacturing industry. Improper hobbing and/or shaving, improper handling or distortion in heat treating result in poor profile, lead, as well as, nicks and burrs. These imperfections are found in the hardened gears but there has been no truly economical way to re-work the gears to correct for major errors in lead or profile.
Soft plastic hones impregnated with an abrasive and tungsten carbide coated hones were introduced to re-work gears. Speeding, lapping and hand operations for burr and nick removal have been used when required.
The plastic hones, being relatively soft, would follow the form already on the gear, thus giving no correction of lead or profile. The hone did improve the surface finish but would not remove significant amounts of metal. Honing gears with large lead errors or nicks would cause the teeth of the plastic hones to be chipped or broken out. Thus plastic hones are being used primarily as a surface finishing tool.
Tungsten carbide coated hones improved the situation by being able to remove small imperfections but possess such a relatively short useful life that they are rarely employed for significant stock removal which is required in major corrections.
The long established problem of economically correcting significant errors in lead, profile and oversize as compared to the conventional techniques of gear grinding or complete re-work has not been solved prior to the present invention.
Particularly in those gear manufacturing areas which require very high quality and accuracy of gear form, present techniques of correcting lead or profile errors are very expensive processes in hardened gears.
However, the improvement in gear performance, quieter running, and longer life make correction of these errors to a high degree worthwhile, particularly if accomplished in a less expensive manner compared to present techniques.
Gear hones presently used in the industry, can in some instances remove up to 0.002 inches of stock as measured over pins in the gear teeth, however, the material is removed substantially in a uniform manner. Thus if there is a lead or profile error prior to honing, there will be the equivalent error after honing. However, in these prior hones, substantial stock removal requires much greater honing times and greatly increases cost as the hone life per gear worked is dramatically decreased. Therefore, prior type hones are seldom recommended for use in applications requiring significant or major stock removal.
With specific reference to prior attempts to employ mono-layer diamond hones, reference is made to British Patent No. 1,392,704. In this patent, general reference is made to the historical problem of correcting a gear tooth shape and to an unsupported allegation that a diamond hone can accomplish this task, however the detailed specification is devoted to fine surface finishing which is similar to that which is accomplished with the multi-layer plastic hones or tungsten carbide hones.
Further, the recommended sizes of the diamond particles employed for optimum performance are only useful for fine surface finishing and not for any significant removal of metal sufficient to provide shape correction in any practical manner.
Also there is no mention whatever in this patent of the unique geometry of the gear hone teeth as disclosed in the present invention which has been found to be necessary to obtain desirable and commercially acceptable results in the final gear tooth shape.